BRIDGE BASICSBRIDGE BASICS

THERE ARE THREE MAIN TYPES OF BRIDGES:

1. BEAM BRIDGE 2. ARCH BRIDGE3. SUSPENSION BRIDGE

• THE BIGGEST DIFFERENCE BETWEEN THE THREE IS THE DISTANCES THEY CAN EACH CROSS, OR SPAN.

WHAT ALLOWS AN ARCH BRIDGE TO SPAN GREATER DISTANCES THAN A BEAM BRIDGE, OR A SUSPENSION BRIDGE TO SPAN A DISTANCE OF NEARLY 7 TIMES THAT OF AN ARCH BRIDGE?

WHAT ALLOWS AN ARCH BRIDGE TO SPAN GREATER DISTANCES THAN A BEAM BRIDGE, OR A SUSPENSION BRIDGE TO SPAN A DISTANCE OF NEARLY 7 TIMES THAT OF AN ARCH BRIDGE?

THE ANSWER LIES IN HOW EACH BRIDGE TYPE DEALS WITH TWO IMPORTANT FACTORS CALLED………

COMPRESSION AND TENSION:

• COMPRESSION IS A FORCE WHICH ACTS TO COMPRESS OR SHORTEN THE THING IT IS ACTING ON.

- BUCKLING

• TENSION IS A FORCE WHICH ACTS TO EXPAND OR LENGTHEN THE THING IT IS ACTING ON.

- SNAPPING

The Beam Bridge- A beam bridge is basically a rigid horizontal A beam bridge is basically a rigid horizontal structure which is resting on two piers, one at structure which is resting on two piers, one at each end. each end. - The weight of the bridge and any traffic on it is - The weight of the bridge and any traffic on it is

directly supported by the piers. The weightdirectly supported by the piers. The weight is is

traveling directly downward.traveling directly downward.

The Beam Bridge- A beam bridge is basically a rigid horizontal A beam bridge is basically a rigid horizontal structure which is resting on two piers, one at structure which is resting on two piers, one at each end. each end. - The weight of the bridge and any traffic on it is - The weight of the bridge and any traffic on it is

directly supported by the piers. The weightdirectly supported by the piers. The weight is is

traveling directly downward.traveling directly downward.

COMPRESSION IS MANIFESTED ON TOP OF THE BRIDGE DECK

TENSION CAUSES THE LOWER PORTION OF THE BEAM TO LENGTHEN

DISSIPATION- FORCES ARE DISPERSED OR SPREAD OUT BY INCREASING THE HEIGHT OF THE BEAM.

TYPES:TYPES:- DURING INDUSTRIAL REVOLOUTION WOODEN BRIDGES WERE BEING REPLACED BY IRON AND IRON/WOOD COMBINATIONS.

DESIGNED BY WILLIAM HOWE IN 1840

WORLD’S LONGEST BEAM BRIDGE LAKE PONCHARTRAIN CAUSEWAY, LOUISIANA

- ALMOST 24 MILES LONG - SPAN BEAM BRIDGE

ARCH BRIDGEARCH BRIDGE ONE OF THE OLDEST TYPES OF BRIDGES

WEIGHT OF THE ARCH BRIDGE IS CARRIED OUT WARD ALONG THE CURVE OF THE ARCH TO THE SUPPORTS, CALLED ABUTMENTS.

ABUTMENTS CARRY THE LOAD AND KEEP THE ENDS OF THE BRIDGE FROM SPREADING OUT.

ARCH BRIDGES ARE ALWAYS UNDER COMPRESSION. THE FORCE OF COMPRESSION IS PUSHED OUTWARD ALONG THE CURVE OF THE ARCH TOWARDS THE ABUTMENTS.

TENSION IS NEGLIGIBLE. THE NATURAL CURVE OF THE ARCH DISSIPATES THE FORCE OUTWARD REDUCING THE TENSION ON THE UNDERSIDE.

DEGREE OF CURVE, EFFECT OF TENSION UNDER

TYPES:TYPES: AFTER ALL AN ARCH IS AN ARCH, BUT SOME ARE:

- ROMAN (AND AQUEDUCTS), BAROQUE, AND RENAISSANCE 

 Arch Bridge

Bixby Creek Bridge, Monterey, CA

SUSPENSION BRIDGESUSPENSION BRIDGE

CABLES (ROPES OR CHAINS) ARE STRUNG ACROSS AS THE DECK IS ATTACHED OR “SUSPENDED” FROM THESE CABLE.

TWO TALL TOWERS THROUGH WHICH THE CABLES ARE STRUNG.

TOWERS SUPPORT MAJORITY OF THE ROADWAYS WEIGHT.

CompressionThe force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers which dissipate the compression directly into the earth where they are firmly entrenched.

TensionThe supporting cables are literally stretched from the weight of the bridge and traffic as they run from anchorage to anchorage. The anchorages are also under tension, but since they, like the towers are held firmly to the earth, the tension they experience is dissipated.

TYYPES:TYYPES: 1) “A” SHAPE (CABLE STAYED BRIDGE):

- CABLES RUN FROM ROADWAY UP TO SINGLE TOWER.

FORCES:

A cable-stayed bridge near Savanah, Georgia

TYPES:TYPES:

2) “M” SHAPE- TWO TOWERS FOUR ANCHORAGES

A classic suspension bridge in New York city (Manhattan)

Suspension bridgeGolden Gate Bridge, San Francisco, CA

ENGINEER JOSEPH STRAUSS

AKASHI KAIKYO BRIDGE

(Longest Free Standing Bridge)

KOBE, JAPAN

LENGTH: 12,828

2 Km

1995 Kobe earthquake had its epicenter right between the two towers of the Akashi Straits Bridge. The original planned length was 1990 meters for the main span, but the seismic event moved the towers apart by almost a meter. Since construction of the deck had not yet begun, the changes were easily accommodated in the slightly altered final

design.

HOW BRIDGES STACK UP…..HOW BRIDGES STACK UP…..

TACOMA NARROWS BRIDGE

“GALLOPING GERTIE”

TACOMA NARROWS BRIDGE

“GALLOPING GERTIE”

OPENED FOR TRAFFIC IN 1940, AT THE TIME THE 3RD LONGEST SUSPENSION BRIDGE IN THE WORLD

FOUR MONTHS AFTER OPENING IT COLLAPSED IN A WIND OF 42 MPH…

…BELIEVED TO BE CAUSED BY REASONANCE

TRY AGAIN,TRY AGAIN, RECONSTRUCTION BEGAN NINE YEARS LATER

- WIDER WITH DEEP STIFFENING TRUSSES

New Tacoma Narrows Bridge

As new strong, lightweight synthetic materials become more common, ever more impressive bridges will be built. The current “next step” is to bridge the Straits of Gibraltar.

What does the immediate future hold?What does the immediate future hold?